With this change we save a copy of of scroll state at the time of
recording a display list, instead of actual ScrollState pointer that
could be modifed by the main thread while display list is beings
rasterized on the rendering thread, which leads to a frame painted with
inconsistent scroll state.
Fixes https://github.com/LadybirdBrowser/ladybird/issues/4288
`DisplayListPlayer::execute_impl()` can receive null surface if it was
invoked to rasterize nested display lists (we use them for iframes). In
this case we should not call `flush()` by the end of execution and wait
until outer display list execution will do that.
The Skia Ganesh backend we currently use doesn't support painting from
multiple threads, which could happen before this change when the main
thread used Skia to paint on the HTML canvas while the rendering thread
was working on display list rasterization.
Fixes https://github.com/LadybirdBrowser/ladybird/issues/4172
Deleteing set_surface() makes DisplayListPlayer API a bit more intuitive
because now caller doesn't have to think whether it's necessary to
restore previous surface after execution, instead DisplayListPlayer
takes care of it by maintaining a stack of surfaces.
This adds a command for saving the current layer of the canvas.
This is useful for painting content onto a blank background in
isolation and later compositing it onto the canvas.
These operations should still apply even if they are off screen, because
they affect painting of things outside of their bounding rectangles.
This commit makes us always apply these, regardless of if they are in
the visible region. However, if they are outside that region, we
replace them with simple clip-rect commands, which have the same
effect (not painting anything) but are cheaper than computing a full
mask bitmap.
